Underwatering, overwatering can cause leaves to wilt

A: Donut peach — sometimes called bagel peach, Saturn peach, pan tao peach and a bunch of other names — is a good choice for our climate and soils. It is a novelty but delivers very sweet fruit great for eating fresh. Birds love the fruit, too, a problem that I have mentioned in the past as well as how to avoid it.

Thanks for the pictures. I understand it is still in the container, and you will plant it in the ground soon.

For leaf wilting to occur, something is stopping the water from reaching the leaves. This could be a soil problem, root damage, stem damage or direct damage to the leaves. Obviously, a lack of water or watering too often that the roots suffocate can cause wilting.

A common problem this time of year is applying fertilizer or strong compost too close to the trunk. This can cause the leaves to wilt because of the high nutrient content (salts) in fertilizers and many rich composts. If applied next to the trunk or against it, it can cause plant wilting followed by death.

Apply fertilizers and compost no closer than 12 inches from the trunk. If the container is smaller than this, then use a very small amount and apply it more often.

Check for borer damage on the trunk. I had trees coming from the nursery, both container and bare root, with borers already in the trunk. If your tree had borers in it the same season you bought it, the borer came with the tree when it was bought. No extra charge!

Spray the trunk with water from a spray bottle several times until the stem is soaked. If the borer is active, you will see globs of brown or dark red sap coming from the stem. Sometimes I can squeeze the stem with my first two fingers, and I can feel sponginess where the borer is feeding just under the bark. Dig it out with a sanitized sharp knife and let it heal.

It is possible that spray drift from weedkillers could do it, but I may be grasping for straws with that one.

Q: Can you use lava rock as a ground cover around any shrubs? I am thinking particularly of Japanese boxwood.

A: Lava rock was used extensively in Las Vegas landscapes as a surface covering before desert landscaping became popular. Desert landscaping uses specialty rock mulch of different colors and sizes, and its use has pushed lava rock out of this niche.

Lava rock has some interesting qualities, different from the rock we have available to us today. It can be a good alternative to rock mulch.

Lava rock, or any rock mulch for that matter, would not be a good choice around Japanese boxwood. Japanese boxwood grows better in soils amended with compost and the soil covered in organic wood mulch, not rock mulch or lava rock.

Using rock mulch or not depends on the plants. I am frequently asked which plants can tolerate rock mulch and which ones cannot. That’s difficult to explain unless you know where the plant originated.

Plants that originate from desert climates can generally handle rock mulch better than those that did not. Sometimes that information is difficult to find.

Boxwoods come from nondesert environments. They don’t come from the “deserts of Japan.” They come from wetter and cooler climates than ours, so avoid placing them in west and south exposures. Amend the soil at the time of planting with compost and cover the soil with something that decays, such as wood chip mulch, which adds organics back to the soil.

Lava rock falls into the category of a rock mulch. It does break down over time adding minerals to the soil, but it adds no organics. The same problem occurs as with other rock mulches.

Over a few years, the compost added during planting is gone, replaced by the minerals without organics. These soils may be rich in minerals but lack the physical properties needed for good drainage, root growth and the chemistry required for nondesert plants to thrive.

Q: I am considering planting three boxed African sumacs along a 40-foot block wall behind a 1½-foot retaining wall. Is this feasible? How far away should they be from the block wall? Is there a better option for shade that isn’t poisonous to dogs and that has no invasive root issues?

A: If this tree is to be planted by landscapers in a package deal from the nursery, be aware that very small holes are dug, and little is added to amend the soil; a hole large enough for the tree roots to fit into and not much else. That may work in the organic soils of Kansas, but not in the Mojave Desert with soils that contain less than 1/10 of 1 percent organics. Definitely not sustainable.

This can lead to disaster in a few years. The planting hole should be dug three times the width of the container or box. This is probably a 24-inch boxed tree so a hole 72 inches in diameter would be the smallest width recommended.

In most cases, the soil taken from the hole — minus rocks larger than a golf ball — can be mixed with it at approximately 50 percent by volume. In other words, a 1-1 ratio of good compost and soil. If you use good compost, you will not need a fertilizer the first season.

The tree is carefully leaned over on its side, and the bottom of the box is removed and lowered into the hole. The sides of the box are then removed and taken from the hole.

As the tree is backfilled around its roots with the soil and compost mix, water from a hose should be making a slurry around the root ball to remove air pockets. You will see bubbles coming from the slurry as air is pushed out.

After the tree has been planted and watered, construct a 4-inch-deep level basin around the planting hole, so that it holds water. Hand water these trees with a hose, filling the basin entirely, three or four times over the next two weeks in addition to normal irrigations. Yes, it is needed in our climate and soils.

Once the tree has been watered and established (no more air bubbles coming from the soil, and the tree is held firmly upright), turn it over to the irrigation system full-time. Water a 24-inch boxed tree twice a week with 15 to 20 gallons of water applied at each irrigation; 15-gallon tree, 8-10 gallons; 5-gallon tree, 3-5 gallons. Stake the tree if needed.

Eighty percent of all landscape plants are poisonous. If your dogs eat enough of any of your plants, they can get sick.

Plant them no closer than 6 to 8 feet from any wall, patio or sidewalk. This tree can grow to 40 feet and consume a fair amount of water. These trees, because of their canopy shape, are not intended for planting along walls taller than 6 feet.

Wet the soil from your irrigation system away from the wall, so roots will grow less toward the wall. Consult sites such as the plant list found at the Las Vegas Valley Water District and consult with your local nursery about availability of plants that you like.

Bob Morris is a horticulture expert living in Las Vegas and professor emeritus for the University of Nevada. Visit his blog at xtremehorticulture.blogspot.com. Send questions to Extremehort@aol.com.